The primary objective of this proposal for a Program Project Grant in Viral Tumorigenesis is to understand the molecular mechanisms whereby viruses cause cancer. Related objectives are to understand control of viral gene expression and DNA replication in animal cells and enzymatic mechanisms of genetic recombination. This project concentrates on 1) model DNA viruses which cause cancer in animals and transformation of cells to tumorigenicity in culture, 2) parvo-viruses which present interesting problems in gene expression and replication, and interfere with oncogenic viruses, and 3) related studies of molecular mechanisms of genetic recombination in especially tractable bacterial systems. The application reflects the overlapping interests and cooperative research efforts of five investigators, whose laboratories are contiguous within the Department of Microbiology at the Johns Hopkins University School of Medicine.